Influence of engineered self-healing systems on ASR damage development in concrete

Supplementary cementing materials (SCMs) have proven effective in minimizing alkali-silica reaction (ASR) development. In addition, crystalline admixtures (CAs) have been identified as potential solutions to counteract damage in concrete. However, limited data on this topic is available in the literature. This study investigates the impact of CA on concrete damage and is divided into two phases: 1) the effectiveness of CA in self-healing cracks and restoring the mechanical properties of mechanically damaged concrete; 2) it explores concrete mixtures incorporating a wide range of binder compositions (i.e., general use type cement, silica fume, fly ash, slag and Metakaolin) and chemical admixtures (i.e., commercially available CAs and modified versions) in conditions enabling ASR development. Both phases involve microscopic/mechanical analyses to assess the effects of CA on damage, and comparisons with concrete mixtures without CAs are made. The results reveal that CA enhanced the self-healing of cracks up to 82 % of cracks in cement paste (115 % higher values than concrete mixtures without CA) and restored 69 % of compressive strength. Furthermore, although CAs could change the damage mechanism of ASR, they did not “safely” mitigate it. However, combining SCMs and CAs effectively reduces ASR-induced expansion

Condition assessment of two prestressed concrete slabs after 60 years in service

Two concrete deck slabs extracted from a Canadian bridge have been evaluated using non-destructive testing (NDT), followed by destructive testing. Throughout its service life, the bridge experienced harsh environmental conditions with frequent freeze-thaw cycles, hot and humid summers, and the use of de-icing salts during winters. This study presents the preliminary results of an exhaustive condition assessment of two prestressed concrete slab panels, where NDT techniques (visual assessments, electrochemical and concrete soundness tests) have been conducted prior to destructive testing. Although visual inspection did not indicate poor concrete quality, the results of the ultrasonic pulse velocity testing showed that both concrete slabs are of poor quality and may be suffering from internal defects. Chlorides may have also been introduced through the strand conduit anchor points. These findings raise concerns regarding the structural integrity of corrosion-affected members

Development of a durability indicator to forecast the efficiency of preventive measures against external sulphate attack

Currently, the C3A content of binders is considered the most important factor contributing to external sulphate attack (ESA) deterioration. However, portlandite is also deemed to play a major role in ESA development. Yet, there are very few researches on this topic. This paper evaluates physical (i.e., induced expansion and mass variation, ultrasonic pulse velocity, dynamic modulus of elasticity, modulus of rupture and compressive strength) and chemical (i.e. X-ray diffraction and thermogravimetry) properties of seven mortar mixtures presenting distinct binders (i.e. cement types, inert fillers and supplementary cementing materials) and exposed to different sulphate solutions (i.e. sodium and magnesium). Correlations are conducted between data obtained in the laboratory, and a theoretical approach to describe cementitious mixtures’ susceptibility against ESA is then proposed. Results show that the proposed durability indicator (i.e., predicted portlandite amount and potential of ettringite formation) are well correlated with ESA-induced expansion and damage. Moreover, the influence of portlandite on ESA seems to depend on the type of sulphate attack (i.e., Na2SO4 or MgSO4). Finally, highly reactive SCMs and consequent higher portlandite consumptions seem to increase the overall deterioration due to MgSO4 exposure